One particularly advantageous application of the invention relates to the manufacture of lining elements, such as blades, of a sectored-type curing or vulcanizing mould for vehicle tires.
This type of mould mainly comprises two shells that each mould one of the lateral sidewalls of the tire, a plurality of sectors that mould the tread of said tire and are radially movable between an open position and a closed position of the mould. The shells and the sectors define an inner space that is intended to be brought into contact with the unvulcanized green form of the tire. In order to form the tread patterns, blades are attached to the sectors of the mould and protude into this inner space. For further details on a mould comprising such blades, reference could for example be made to documents EP-B1-1 758 743 and US-A1-2002/0139164.
The advantage of manufacturing by selective melting of superposed layers of powder, more commonly referred to as sintering, mainly lies in the fact that the shape of these blades may be modelled by a computer and that the blades may then be manufactured on the basis of this modelling by computer control of the beam of energy. In addition, this technique is highly suitable for the manufacture of elements of small sizes and of complex shapes, such as mould lining blades, which are difficult to manufacture with other processes.
When the selective melting is carried out by a laser beam, it is referred to as laser sintering. The laser sintering technique consists in manufacturing the blade layer after layer, by stacking the layers of powder, which are consolidated and fused on top of one another by the laser beam, in a stacking direction. The term “powder” is understood to mean a powder or a mixture of powders. The powder may for example be metallic or mineral, for example ceramic.
Conventionally, in order to ensure the preparation of the bed of powder prior to the sintering or melting operation, a layering device is used. Such a device mainly comprises a cylinder or roller capable of distributing the powder as a layer on a manufacturing plate. For more details, reference may be made for example to the patent application FR-A1-2 974 316.
The first layer is deposited then welded directly to the manufacturing plate. The other layers are then formed successively so as to obtain a stack starting from the first layer.
Once the blade is formed, it is necessary to detach it from the manufacturing plate, for example by cutting by electro-erosion by wire. This detachment may lead to a deformation of the blade in so far as the existing mechanical stresses between the various stacked layers may be modified.
In order to overcome this drawback, patent application FR-A1-2 961 741 recommends providing overthicknesses formed integrally with the blade and that form reinforcers. This solution is effective for guaranteeing that the blades retain their shape after detachment from the manufacturing plate on which they were manufactured.
However, even with such reinforcers, under the effect of the forces applied by the layering device on each pass over the powder layers, vibrations, deformations and/or deteriorations of the blades in the process of being manufactured may occur, which may give rise to the appearance of stress concentrations and microcracks. This is especially the case for the blades having a relatively small cross section.